1. Field of the Invention
The present invention relates to an electronic component-embedded board and a method of manufacturing the same.
2. Description of the Related Art
In recent years, with the progress in electronics technology, there has been a growing demand towards higher density in printed circuit boards. As such, multilayer printed circuit boards in which are laminated pluralities of wiring patterns and insulating layers are becoming widely used.
Conventionally, for the purpose of increasing productivity, printed circuit boards used in these types of applications are manufactured in a “multiple dice from one substrate” manner in which, for example, an approximately 300 mm to 500 mm square worksheet (assembly substrate) provided with a plurality of wiring pattern groups (wiring layers) for printed circuit boards is separated into individual dice by dicing or the like to obtain a plurality of printed circuit boards (individual substrates, dice, or bodies). Multi-layering of the worksheet is normally achieved by alternately building up wiring patterns and insulating layers. Then, generally, a wiring pattern or the like is formed using a subtractive method or an additive method while an insulating layer is formed by thermal curing of a thermosetting resin.
With the conventional worksheet manufacturing method described above, warpage of a worksheet inevitably occurs due to stress applied during the formation of the insulation layers. Accordingly, in order to suppress warpage of the worksheet, for example, Japanese Patent Laid-Open No. 09-135077 and Japanese Patent Laid-Open No. 2005-167141 propose a manufacturing method in which a plurality of wiring pattern groups (wiring layers) for printed circuit boards as well as a frame-like conductive pattern that surrounds the plurality of wiring patterns are provided on a worksheet, whereby resin is applied so as to cover the wiring patterns and the frame-like conductive pattern to be subsequently cured.
[Patent Document 1] Japanese Patent Application Laid-Open No. 09-135077
[Patent Document 2] Japanese Patent Application Laid-Open No. 2005-167141
On the other hand, more and more mobile devices typified by, for example, a mobile terminal such as a mobile telephone are mounted with a so-called electronic component-embedded board in which a semiconductor element (die) in a bare chip-state is mounted as an active element on a substrate constituted by a single or a plurality of resin layers. Additionally, in order to meet the needs towards higher performances and smaller sizes in electronic devices, progress has been made in modularization involving mounting, in high density, active elements such as a semiconductor IC or the like and passive elements such as a varistor, a resistor, and a capacitor. Furthermore, there has been an ever-increasing demand towards a thinner profile for a module mounted with at least one of active elements and passive elements. As such, there is a pressing need for further thinning.
Under such circumstances, after applying the conventional worksheet manufacturing method described above when manufacturing an electronic component-embedded board, contrary to expectations, it was found that warpage of the electronic component-embedded board had not been suppressed and, rather, a deteriorating trend existed in comparison to the manufacturing of substrates not embedded with an electronic component. Moreover, according to findings by the present inventors, when thinning an electronic component-embedded board to a thickness of 500 μm or less and, in particular, to a thickness of 400 μm or less, excessive warpage of the order of several tens of millimeters tends to occur with respect to the entire worksheet. An occurrence of such an excessive warpage of the worksheet leads to the occurrence of manufacturing/processing problems such as, for example, conveyance failure, reduction in positional accuracy during build-up, and reduction in mounting positional accuracy during surface mounting, which causes not only a decline in process yield but also a decline in the mounting reliability of the obtained electronic component-embedded board.
At the same time, the warpage of a worksheet is conceivably suppressible through the formation an insulating layer in a state where the shape of the substrate is kept flat by grasping the worksheet from the outside using supporting members or the like. Unfortunately, in this case, the necessity of a grasping process each time an insulating layer is formed complicates manufacturing/processing and reduces productivity and economic efficiency.
The present invention was made in consideration of such circumstances, and an object thereof is to provide a method of manufacturing an electronic component-embedded board that does not require complicated processes, which is capable of suppressing the occurrence of warpage at low cost, and which offers high productivity and economic efficiency, and also to provide an electronic component-embedded board.